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To create a dynamic and multi-pane user interface on Android, you need to encapsulate
UI components and activity behaviors into modules that you can swap into and out of
your activities. You can create these modules with the Fragment class, which
behaves somewhat like a nested activity that can define its own layout and manage its own
lifecycle.

When a fragment specifies its own layout, it can be configured in different combinations with
other fragments inside an activity to modify your layout configuration for different screen
sizes (a small screen might show one fragment at a time, but a large screen can show two or
more).

This class shows you how to create a dynamic user experience with fragments and optimize your
app's user experience for devices with different screen sizes, all while continuing to support
devices running versions as old as Android 1.6.